44.Gastrulation (formation of the three-layered germ disc). Function of the primary streak

Question 1

Gastrulation

Answer 1

Components:
Hensen’s knot (primary knot)
Primary streak

Processes:
-Epiblast proliferation and invagination
-Some epiblast cells differentiate into embryonic endoderm (endoblast)
-Cells between epiblast and endoderm differentiate into mesoderm (mesoblast)
-Mesenchyme forms from lateral mesoderm
-Remaining epiblast cells form ectoderm (ectoblast)

Question 2

Function of the primary streak

Answer 2

It determines the axes of the body of the embryo

 front-back
 ventro-dorsal
 left right

 Activates the formation of the mesoderm in the early stage
 It usually disappears by the end of the fourth week (day 25-26).
 Remnants can persist and lead to large tumors - sacro-coccygeal
teratoma